The gases which are contained in the crankcase of a combustion engine contain a plurality of various particulate impurities. Since the crankcase is vented and thus in contact with the surrounding atmosphere, these particulate impurities would reach the surrounding atmosphere if the crankcase gas is not cleaned. The requirements from the authorities in this area are now increasing in many countries in order to prevent uncleaned crankcase gases from being discharged in an uncontrolled manner. A device providing such a cleaning and being of the type initially defined is disclosed in EP-A-1 273 335. By means of the rotating member, the gas may be given the kinetic energy that ensures an efficient separation of the particulate impurities from the gas. The rotating member provides a certain pump effect on the crankcase gas and will thus force the crankcase gas out of the crankcase. This known device is thus not dependent on the generation of a pressure in the crankcase for the discharge and cleaning of the crankcase gas. By means of a simple pressure regulator, the pressure that shall prevail in the crankcase and that varies in different combustion engines may be adjusted in an easy manner. It can however not be excluded that the gas also by means of such a rotating member will contain a small rest amount of particulate impurities in relation to the main amount.
Devices of similar kinds are disclosed in WO2004/001201 and WO2004/022239.
EP-A-685 635 discloses another kind of device for ventilation of the crankcase of a combustion engine. The device includes a separator for cleaning the crankcase gas leaving the crankcase and more precisely for separating oil from the crankcase gas. EP-A-685 635 proposes that the oil separator is designed as an electric filter. The purpose of this oil separator is to separate a main part of the oil that is contained in the crankcase gas. The electric filter of the oil separator may include one of several stages. Furthermore, it is defined in EP-A-685 635 that a further separator may be provided upstream the oil separator. This further separator is a coarse separator for separating a part the oil that is contained in the crankcase gas. The coarse separator may include different kinds of separators and EP-A-685 635 proposes cyclones, rebound separator of fibre separators. All these kinds of separators are passive in the sense that they requires that the gas proper has a certain pressure or a certain kinetic energy that can be used for the separation. A sufficient kinetic energy is however not available in all applications, which, for instance in an engine application, means that the crankcase gas has to be given kinetic energy by means of a pump or there like.
In many applications there are also heavy requirements saying that the separation equipment should be light and require a minimum of space. These requirements, which are especially expressed for motor vehicles, makes it more difficult to provide an efficient and complete separation of particulate impurities.